1. Field of the Invention
The present invention is directed to a method for recording data information on a magnetic recording medium with the assistance of a magnetic write head and of a controllable recording amplifier connected to drive the write head by supplying the data information thereto in the form of binary data signals as well as bias signals superimposed thereon, and to apparatus for implementing the method.
2. Description of the Prior Art
In recording data information on a magnetic recording medium, for example, a magnetic tape or a magnetic disk, it is already well known in the art to supply the data information to be recorded serially to a recording amplifier in the form of binary data signals. This recording amplifier generates a recording current for a magnetic write head, the current being proportional to the data signals. A number of recording methods, for example NRZ, MFM and GCR recording methods, are available for the representation of the data information in the form of binary data signals.
When the recording current, as indicated, is directly proportional to the data signals, then the operation is generally referred to as direct data recording. In magnetic recordings of analog signals, for example, in audio technology, however, it is frequently preferred to superimpose preferably higher frequency bias signals on the analog signal that represents the useful information. The influence of the bias on the actual recording event is complex and can only be presented by way of models. What is merely to be indicated here is that the remanent magnetization on the magnetic recording medium should be optimally high and should thereby be linearly proportional to the recording field strength. As known, however, standard magnetic recording media generally have a highly non-linear magnetization characteristic. However, a portion of the magnetic field is produced with the assistance of the bias signals, one therewith succeeding in linearizing the recording event in view of the magnetic field portion that corresponds to the information signal. With an unidentifiable bias portion, in combination with a magnetic field portion corresponding to the information signal, one therefore succeeds in eliciting a magnetization value that is proportional to the information signal.
Of course, such a linearization of the magnetic recording event when recording analog information signals is of particular significance since the reproduction quality is directly dependent thereon. The requirement for high linearity is initially less critical in the magnetic recording of data information in the form of binary data signals since the overall information is stored in such cases in the form of discrete magnetization conditions or, more precisely, in the form of magnetization flux changes. For this reason, data information is currently still frequently magnetically recorded with a direct recording method.
The magnetic recording of data information with the assistance of a high-frequency pre-magnetization, however, also has advantages in digital data recording, particularly when high recording densities are desired as presented, for example, in the U.S. Pat. No. 4,202,017, fully incorporated herein by this reference. In accordance therewith, disturbances also occur in digital data recording having high recording densities, particularly during the read-out event, these disturbances to be attributed to the influence of flux changes adjacent to one another. This is expressed as a peak shift with corresponding distortion of the read output signals, whereby the amplitude of the read output signals can also be great. According to the known technical teaching, this effect can be reduced in that an alternating current is superimposed on the recording current that corresponds to the data signals to be recorded, being superimposed thereon for bias. The amplitude of the alternating current is selected such that the magnetization field strength in the recording medium is approximately equal to its coercivity. When the amplitude for the data signal changes is then selected such that it essentially corresponds to that of the bias signals, then the sum of the two signal amplitudes produces a recording in the saturation region.
The European application 0 030 644, for example, discloses a similar technique. In the magnetic storage device for digital recording disclosed therein, high-frequency bias signals are superimposed on the data signals in a synchronized manner. As a consequence of this bias, the amplitude of the data signals to be recorded can be reduced, so that a cross talk from recording magnetic heads to reading magnetic heads can be prevented during the recording event. Furthermore, the recording event is linearized, due to this bias, so that the changes of the data signal read out correspond to the changes of the magnetization on the recording medium can be more accurately recognized.
The situation, however, is such that the effect of the peak shift in a given recording density is dependent not only on the amplitude of the data signals to be recorded, i.e. on the data recording current in such fashion that the peak shift arises with increasing signal amplitudes. The effect of peak shift, on the contrary, is also dependent on the coercivity of the recording medium. Given this influencing variable, the peak shift becomes all the lower, the higher the coercivity of the recording medium. The coercivity of the magnetic recording media, magnetic tapes of different manufacturers, for example, however, is not uniform and is not even necessarily completely uniform over the entire length of a magnetic tape. Added thereto is that the coercivity of a magnetic recording medium is dependent on temperature, i.e. decreases with increasing temperature.
As indicated above, each definition of the amplitude of bias signals with reference to the data signals to be recorded strives for a compromise that yields an optimally-low peak shift of the read output signals given an optimally-high recording signal amplitude. When the relationship between bias current and data recording current has been fixed in this manner in a storage device, then it is unavoidable that the optimum value for a minimum peak shift is normally rarely achieved, since the manufacturer of the storage device has no influence on the temperature at which recording with this device is undertaken on recording media having different coercivities.